1. Field of the Invention
The present invention relates to a laser beam scanning method for laser activation and crystallization for a thin film transistor substrate in a large area-liquid crystal display.
2. Discussion of the Related Art
Laser beam scanning is used to recover or recrystallize a part of a polycrystalline silicon layer which becomes amorphous due to doping with ions, or to crystallize an amorphous silicon layer.
In general, these processes (referred to as activation of the silicon layer using laser) proceeds by supplying a surface of the layer with laser energy by scanning the layer repeatedly with a laser beam having predetermined spatial and energy profiles.
FIG. 1 shows schematically laser scanning according to a technique of the related art. FIG. 2 shows schematically the spatial profile 21 and the energy profile 22 of the laser beam in the length direction of the spatial profile. The laser beam 13 which has an elongated spatial profile 21 is generated by a laser equipment known in the art. The energy profile 22 of the laser beam is substantially flat along the entire length of the beam and has an elongated step shape with steep edges.
Referring to FIG. 1, laser scanning is carried out by irradiating a thin film 10, such as an amorphous silicon film, with the laser beam 13 at a predetermined repetition rate and translating the thin film 10, thereby scanning the whole surface of the thin film. The translating direction of the thin film is opposite to the scanning direction of the laser beam.
However, the length of the laser beam generated by known laser equipment has an upper limit. Typically, the length of the laser beam is about 200-300 mm with a width of about 0.3-2.0 mm. Therefore, when scanning a large area silicon film that is wider than the length of the laser beam, the entire surface of a large area film cannot be irradiated with a single scanning of the laser beam. An example of such a large area film is a wide vision LCD panel having a diagonal dimension of 12.1 inches or more.
Accordingly, the present invention is directed to a laser beam scanning method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide a laser beam scanning method which supplies a large area substrate with uniform laser energy.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a laser beam scanning method, wherein the laser beam has a spatial profile of an elongated rectangular shape and a substantially flat energy profile, the end portions of the energy profile having energy slope regions, the energy slope being defined by the ratio of the laser energy density to the width of the slope region.
Another aspect of the present invention provides a laser beam scanning method, in which a large-area film is irradiated by a laser beam scanning across the film two or more times, to provide laser energy to the whole large-area film, the laser beam being displaced relative to the film in a direction perpendicular to the scan direction before each subsequent scan. The laser beam has a spatial profile having an elongated rectangular shape along an longitudinal axis, and a substantially flat energy profile along the longitudinal axis, where the end portions of the energy profile have energy slope regions, the energy slope being defined by the ratio of the laser energy density and the width of the slope region. The energy slope regions of the successive laser beams are selectively overlapped to supply the substrate with uniform laser energy.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.